1. Field of the Invention
This invention relates to a mobile communication terminal and a method of controlling transmission power for a multiplex radio communication system to send different pieces of information through two or more channels simultaneously.
2. Description of Related Art
Proposed recently in the field of mobile communication are multiplex radio communication systems to send different pieces of information through two or more channels simultaneously.
One of such systems is W-CDMA (Wideband Code Division Multiple Access) system of 3GPP (Third Generation Partnership Project).
3GPP defined additionally an HSDPA (High Speed Downlink Packet Access) system to raise the transmission rate of downlink data from a base station to mobile communication terminals. HSDPA and information about quality of received signals monitored by mobile communication terminals have made possible adaptive modulation and adaptive encoding. Besides, by frequently sending ACK (acknowledge) and NACK (unacknowledge) to the base station, retransmission and composition in high-speed physical layers are possible. ACK means normal reception of signals; NACK, abnormal reception of signals. As a result, the service of high-speed downlink data transmission has been materialized.
[Example of Construction of Conventional Mobile Communication Terminal]
FIG. 6 shows an example of construction of a conventional mobile communication terminal of the W-CDMA system. In FIG. 6, only the main components are shown, the other ones such as filters omitted.
First of all, the flow of outgoing signals is described.
In FIG. 6, the DPDCH (Dedicated Physical Data Channel) is a channel to send out signals. The data of the DPDCH are produced by undergoing retransmission/correction processing in an RLC (Radio Link Control), which is one of the function blocks of a CPU/DSP (Central Processing Unit/Digital Signal Processor) 116, and being channel-coded by a DPDCH encoder 121. Retransmission/correction means sending them to it again if data received by a mobile communication terminal are erroneous. The retransmission/correction of data of the DPDCH is realized in the RLC. The retransmission/correction requires a buffer to store transmitted data. In FIG. 6, a memory 140 connected to the CPU/DSP 116 is the buffer. Because retransmission takes time, retransmission or correction of data, such as voice data, requiring a short delay time does not take place. The DPCCH (Dedicated Physical Control Channel) is a channel to send out information to the receivers of the information for the correction of phases and the estimation of the quality of received signals. The HS-DPCCH (High-Speed Dedicated Physical Control Channel) is a channel to send the following information for HSDPA to the base station. The signals of the DPDCH, DPCCH, and HS-DPCCH are sent to a diffusion unit 101.
The signals of the HS-DPCCH have frame structure shown in FIG. 7. The length of one frame “Tf” is 10 ms. Each frame includes a plurality of subframes. The length of each subframe is 2 ms. Each subframe includes an HARQ (Hybrid Automatic Repeat Request)-ACK section and a CQI (Channel Quality Indicator) section. Indicated in the HARQ-ACK section is ACK or NACK. The base station sends out the next data in the case of ACK and re-sends out the same downlink data in the case of NACK. Indicated in the CQI section is information about quality of received signals. The base station determines the modulation factor and the encoding rate of downlink data based on the CQI and other information. The size of the HARQ-ACK section is 2,560 chips. Only when the mobile communication terminal receives signals addressed to it, ACK or NACK is sent out by the HARQ-ACK section. The size of the CQI section is 5,120 chips. Only when the network side designates time intervals, CQI's are sent out at the time intervals.
The signals of the DPDCH inputted into the diffusion unit 101 are sent to a multiplier 124. The signals of the DPCCH inputted into the diffusion unit 101 are sent to a multiplier 125. The signals of the HS-DPCCH inputted into the diffusion unit 101 are sent to a multiplier 126. The multiplier 124 multiplies the signals of the DPDCH by a channelization code Cd. The multiplier 125 multiplies the signals of the DPCCH by a channelization code Cc. The multiplier 126 multiplies the signals of the HS-DPCCH by a channelization code Chs. Thus, the signals of the DPDCH, DPCCH, and HS-DPCCH are diffused by the channelization codes Cd, Cc, and Chs, respectively, in the diffusion unit 101. Thereafter, the signals of the DPDCH, DPCCH, and HS-DPCCH are sent to an amplitude regulator 102.
In the amplitude regulator 102, the signals of the DPDCH, DPCCH, and HS-DPCCH are sent to multipliers 127, 128, and 129, respectively. The multiplier 127 multiplies the signals of the DPDCH by an amplitude ratio-setting coefficient Kd coming from a transmission-power controller 117 to be described later. The multiplier 128 multiplies the signals of the DPCCH by an amplitude ratio-setting coefficient Kc coming from the transmission-power controller 117. The multiplier 129 multiplies the signals of the HS-DPCCH by an amplitude ratio-setting coefficient Khhs coming from the transmission-power controller 117. Thus, the amplitude regulator 102 regulates the amplitudes of signals of the DPDCH, DPCCH, and HS-DPCCH with the amplitude ratio-setting coefficients Kd, Kc, and Khs, respectively. Thereafter, the signals of the DPDCH are sent, as signals of the I-phase, to an adder 132.
The HS-DPCCH is allocated to the I-or Q-phase depending on the multi-code number of the DPDCH. For example, if the DPDCH is one channel, the HS-DPCCH is allocated to the Q-channel and multi-coded with the DPCCH. In FIG. 6, the signals of the DPCCH and the HS-DPCCH after the setting of the amplitude ratio are added up by an adder 130 and sent, as signals of the Q-phase, to the adder 132.
In the adder 132, the signals of the I-phase and those of the Q-phase are multiplexed. In the example of construction shown in FIG. 6, the transmission-power controller 117 regulates the amplitude ratio-setting coefficients Kd, Kc, and Khs so as to make the power of the multiplexed signals (the power of the base band) a constant value Pbb.
A scrambler 103 scrambles the multiplexed signals with a prescribed scrambling code, and the scrambled multiplexed signals are sent to a D/A (Digital/Analog) converter 104. The D/A converter 104 converts the digital signals to analog signals and sends the analog signals to a DC/AC converter 105. The DC/AC converter 105 converts the DC signals to AC signals. It is assumed for the simplicity of description that the gains of the scrambler 103, D/A converter 104, and DC/AC converter 105 are 0 dB. The AC signals are sent to a variable-gain amplifier 106.
The variable-gain amplifier 106, under the control by the transmission-power controller 117, amplifies the power of the AC signals (the power of signals of the RF band) with a gain G up to the level of necessary transmission power and sends the amplified signals to an antenna 107.
The antenna 107 transmits the signals.
Next, the flow of received signals will briefly be described.
The antenna 107 receives signals. The signals are amplified and down-converted by an RF/IF (Radio Frequency/Intermediate frequency) receiver circuit 108, converted to digital signals by an A/D (Analog/Digital) converter 109, and back-diffused and rake-composed by a rake-finger unit 110. Thereafter, the signals of the channels are sent to decoders 111, 112, and 113 which are provided to correspond to the channels.
An HS-SCCH (High-Speed Signaling Control Channel) decoder 111 decodes the signals of an HS-SCCH, which is a control-signal channel for HSDPA service, and sends the decoded signal to the CPU/DSP 116.
An HS-DSCH (High-Speed Downlink Shared Channel) decoder 112 decodes the signals of an HS-DSCH which is a data channel for HSDPA service. The decoded signals and the result of the checkup of data for errors by a CRC (Cyclic Redundancy Check) unit 115 are sent to the CPU/DSP 116. The HS-DSCH decoder 112 has a buffer for retransmission and composition. By using data stored in the buffer, the above retransmission and composition in physical layers are accomplished.
An other-channel decoder 113 decodes the signals of another channel and sends the decoded signals to the CPU/DSP 116. For example, it decodes the signals of a control channel transmitted in advance of HSDPA service.
A TPC (Transmission Power Control)-bit checker 114 extracts and reads the TPC bits, which are inserted in the channels from the rake-finger unit 110, and sends the results of the reading to the transmission-power controller 117.
If the decoded data can be retransmitted and corrected in the RLC of the CPU/DSP 116, the retransmission/correction processing is made in the RLC. Such retransmission/correction processing requires a buffer; accordingly, the memory 140 connected to the CPU/DSP 116 serves as the buffer, too. If the data of the HS-DSCH can be retransmitted and corrected in the RLC, the retransmission and correction are made in the RLC, in addition to the retransmission and composition in physical layers.
The CPU/DSP 116 holds the values of maximum transmission power Pmax and base-band power Pbb, parameters peculiar to the mobile communication terminal, in an internal memory or the like. Besides, the CPU/DSP 116 collects, from the data of the control channel transmitted in advance of HSDPA service, information about (i) ΔTPC showing how many bits are controlled per one time of transmission-power control, (ii) initial transmission power Pini, (iii) a weighting coefficient βd corresponding to the transmission-power ratio of the DPDCH to the other channels, (iv) a weighting coefficient βc corresponding to the transmission-power ratio of the DPCCH to the other channels, (v) a weighting coefficient βhs corresponding to the transmission-power ratio of the HS-DPCCH to the other channels.
The transmission-power controller 117 calculates the amplitude ratio-setting coefficients Kd, Kc, Khs, and G from Pmax, Pbb, ΔTPC, Pini, βd, βc, βhs, and a TPC_CMD (command) and controls the transmission power ratios and the total transmission power of the channels.
The ΔTPC and the TPC_CMD are parameters relating to closed-loop power control. The closed-loop power control means the control of the transmission power of the communication device on the other end to make the quality of received signals constant. In the closed-loop power control of the transmission power of a mobile communication terminal, the base station calculates the quality of reception from the signals of the DPCCH. If the quality of reception is below the target quality, the base station inserts a command to raise the transmission power as TPC bits into the signals to be sent to the mobile communication terminal. If the quality of reception is beyond the target quality, the base station inserts a command to lower the transmission power as TPC bits into the signals to be sent to the mobile communication terminal. The mobile communication terminal receives the TPC bits and interprets them as a TPC_CMD. The TPC_CMD of “+1” means raising the transmission power, and the TPC_CMD of “−1” means lowering the transmission power. The ΔTPC is the parameter to determine how many bits are controlled per one time of control of transmission power.
[Flowchart of Conventional Control of Transmission Power]
FIG. 8 is a flowchart of the control of transmission power by the transmission-power controller 117. In step S101, ΔTPC, Pbb, Pmax, and Pini are inputted into the transmission-power controller 117. ΔTPC and Pini are given to the mobile communication terminal by the base station and stored in the internal memory of the CPU/DSP 116 in advance of communication, and then they are inputted into the transmission-power controller 117. Each mobile communication terminal has Pbb of a fixed value. Pmax is determined by the specification of each mobile communication terminal. Pbb and Pmax are given to the transmission-power controller 117 by the CPU/DSP 116.
In step S102, TPC_CMDs, βd, βc, and βhs are inputted into the transmission-power controller 117. The CPU/DSP 116 gives the controller 117 a TPC_CMD for each slot and βd, βc, and βhs as the need arises. After step S102, the transmission-power controller 117 proceeds to step S103.
In step S103, the transmission-power controller 117 finds the values of Kd, Kc, and Khs by using the arithmetic expressions shown at step S103 so as to make Pbb constant regardless of any values of βd, βc, and βhs.
In step S104, the transmission-power controller 117 checks to see whether the transmission in process is the initial transmission or not. If it is the initial transmission, the transmission-power controller 117 proceeds to step S105. If it is not, the transmission-power controller 117 proceeds to step S106.
In step S105, the transmission-power controller 117 subtracts Pbb from Pini to find G and proceeds to step S107.
On the other hand, in step S106, the transmission-power controller 117 calculates the gain G to be given to the variable-gain amplifier 106 from the transmission power at the time of previous power control Gprev, the present amplitude ratio-setting coefficient Kc, the amplitude ratio-setting coefficient used for gain-setting at the time of previous power control Kc—rev, and the above TPC_CMD and ΔTPC. The first term of the arithmetic expression shown at step S106 is the set value of the gain at the time of previous power control. The second term of the arithmetic expression is to offset the gain due to the change of Kc occurring as the β's change. The third term of the arithmetic expression is to up and down the gain according to the results of reception-of TPC_CMD's. After the processing of step S106, the transmission-power controller 117 proceeds to step S107.
In step S107, the transmission-power controller 117 stores the value of Kc found in step S103 as an amplitude ratio-setting coefficient Kc—prev to be used for gain-setting at the time of next power control.
In step S108, the transmission-power controller 117 checks to see whether Pbb+G is larger than Pmax or not. If it is, the transmission-power controller 117 proceeds to step S109. If it is not, the transmission-power controller 117 proceeds to step S110.
In step S109, the transmission-power controller 117 subtracts Pbb from Pmax to find G and proceeds to step S110. Thus, in steps S108 and S109, the transmission-power controller 117 regulates the gain G so that the transmission power does not exceed the maximum transmission power Pmax.
In step S110, the transmission-power controller 117 stores the gain G found in step S105, S106, or S109, as the case may be, as a gain Gprev to be used for the next power control and returns to step S102.
Disclosed in the Japanese Unexamined Patent Publication No. 2001-308723 (patent literature 1) is a communication device, which comprises (i) means of multiplying channels by coefficients according to kinds of communication service, kinds of data to be transmitted, or transmission speeds, (ii) a means of multiplexing and modulating the signals of the channels, (iii) a means of varying the transmission power of the multiplexed and modulated signals (hereinafter “gain-varying means”), (iv) a mean of controlling the gain-varying means, and (v) a means of controlling the gain-controlling means so that the maximum transmission power at the time of transmission is controlled by using transmission power which is different from the maximum transmission power which can be set according to the combination of transmission speeds or channels if signals are not transmitted through all the channels simultaneously. With the above construction, the communication device is capable of quality communication in spite of the control of maximum transmission power.
[Patent Literature 1] Japanese Unexamined Patent Publication No. 2001-308723 (FIG. 1)
As described above with reference to FIGS. 6-8, if the transmission power demanded by the base station is beyond the maximum transmission power of the mobile communication terminal, the gain of the variable-gain amplifier 106 is lowered and, as a result, the power levels of the multiplexed channels are evenly reduced below the power level demanded by the base station.
Accordingly, the characteristics of reception of all the channels at the base station deteriorate and, in the worst case, the base station cannot correctly receive information through all the channels. This problem is serious if data cannot be retransmitted or corrected.